Denosumab (brand name: Prolia) is a targeted therapy that is already approved by the U.S. Food and Drug Administration (FDA) for several uses in women. In September 2011, denosumab was FDA-approved to treat bone loss in women taking aromatase inhibitors as part of their breast cancer treatment.
Denosumab is also branded as Xgeva, which is approved to reduce the risk of bone complications (such as fracture) and bone pain caused by advanced-stage cancers, including breast cancer, that has spread to bone. Xgeva is given as an injection under the skin every 4 weeks.
Branded as Prolia, denosumab is approved to treat postmenopausal women diagnosed with osteoporosis at high risk of breaking a bone, or who haven't gotten any benefits from other osteoporosis treatments. Prolia is given as an injection under the skin twice a year. And now, Prolia is approved to help improve bone health in women taking aromatase inhibitors who are at high risk for breaking a bone.
Aromatase inhibitors are hormonal therapies often used in the treatment plan for postmenopausal women diagnosed with either early or advanced breast cancer that is hormone-receptor positive.
The aromatase inhibitors are:
- Arimidex (chemical name: anastrozole)
- Aromasin (chemical name: exemestane)
- Femara (chemical name: letrozole)
Following surgery and other early breast cancer treatments, many postmenopausal women are prescribed an aromatase inhibitor to help reduce the risk of the cancer coming back (recurrence). Hormonal therapy used in this way is called adjuvant hormonal therapy. Adjuvant hormonal therapy for early breast cancer is typically prescribed for 5 years following surgery. The aromatase inhibitors are taken by mouth as a pill once a day.
Hot flashes, night sweats, and joint pain are common side effects of aromatase inhibitors. These medicines can also weaken bones over time and increase the chances of breaking a bone. So it makes sense to use treatment and other steps to strengthen bones while taking aromatase inhibitors.
Denosumab is a targeted therapy, which means it targets specific characteristics of cells. Some targeted therapies, including denosumab, are antibodies that work like the antibodies made naturally by the immune system. Denosumab targets a protein called RANK ligand (RANKL). RANKL affects the activity of certain bone cells called osteoclasts. Osteoclasts help with normal bone breakdown activity to regulate calcium levels. Denosumab blocks RANKL activity and limits osteoclast activity. So denosumab treats osteoporosis by restoring a healthier balance of bone building and bone breakdown. In women who have been diagnosed with breast cancer that has spread to bone, osteoclasts tend to be overactive. These overactive osteoclasts can cause bone pain and bone destruction. By blocking the RANKL protein, denosumab lowers the activity level of the osteoclasts in women whose cancer has spread to bone, reducing their risk of pain and other bone complications.
Possible side effects of denosumab include back, arm, and leg pain; high cholesterol levels; and urinary infections. More serious but much less common side effects include low blood calcium levels, rashes, and severe infections. In rare cases denosumab can cause breakdown of the jaw bone (called osteonecrosis of the jaw). Because of these risks, the FDA requires that anyone considering taking denosumab be carefully evaluated and educated to make sure that denosumab is used appropriately.
While Prolia is the first and only bone-strengthening medicine specifically approved for use to help strengthen bones in women who are receiving an aromatase inhibitor to treat breast cancer, there are other bone-strengthening medicines that doctors can also consider prescribing to maintain or improve the health of bones during aromatase inhibitor treatment.
If you are a postmenopausal woman diagnosed with breast cancer, you should talk to your doctor about your current bone health, and how your treatments might affect your bone health -- especially if an aromatase inhibitor is part of your treatment plan. Ask your doctor what steps you can take to maintain or restore your bone health and whether a treatment such as Prolia might make sense in your specific situation. If bone health is a concern and your breast cancer treatment plan calls for a hormonal therapy, also ask your doctor if tamoxifen could be used as an alternative to an aromatase inhibitor. Unlike aromatase inhibitors, tamoxifen can actually strengthen bones during treatment.
Visit the Bone Health section of Breastcancer.org to learn more about steps you can take to keep your bones strong during and after breast cancer treatment. In this section, you can learn about diet and lifestyle changes for maintaining bone health, as well as bone-strengthening medications.